On an aircraft, such as a rotorcraft, rigid rotor design is typically associated with a small amount of rotor phase lag, that is, the time between the feathering of a blade and the resulting moment is small when compared to a traditional rotor system where approximately 90 degrees of phase lag is expected.
Analysis of a rigid rotor system has shown that the rotor phase lag can vary significantly with speed. In addition to varying with speed, feathering commands introduced at different positions around the rotor will generate moments at different rates. This means that phase lag varies around the rotor as well. As a result, it is difficult to ensure correct on-axis commands for pitching and rolling maneuvers. For the particular case of a coaxial rotor, differential cyclic commands may result in off-axis net moments, and gang cyclic commands may result in undesirable inter-hub moments.